quatic feed production has under-
gone tremendous changes as the
industry has advanced towards
efficiency and sustainability of the
SustainableBusiness.com, published in
2011, stated that aquaculture is in a rapid
industry growth phase, that is “Driving the
scientists' research is the recognition that
aquaculture is one of the fastest growing food
production sectors in the world.
“It has grown at an average annual rate of
8.4% since 1970 and total production reached
65.8 million tons in 2008 according to the
Food and Agriculture Organization of the
United Nations (FAO).
“Today, aquaculture is a US$100-plus bil-
lion industry that provides more than half
of all seafood consumed in the world,
surpassing wild-caught seafood.”
If it is a food fish it can be fed
Let’s review here how the art of
production of feed, for aquatic animals
by extrusion, is prepared and advancing
for various species; predominately the
major species are carp, eel, salmon, trout,
shrimp tilapia, catfish and a collection
of additional species that are regionally
Basically, if it swims and is a food fish
then feeds can be prepared for their
The aspects of the feed are defined
by researchers for those specific species.
Generally, this includes the nutritional
requirements and physical characteristics
required in the feed for select species.
Historically, aquatic feeds were simply
other fish caught to feed the more
valuable marketable species. The shift
occurred when advanced feed produc-
tion methodology was applied which initially
centered on the use of pellet mills. This would
be the art of compounding feed ingredients
into pellets which were sinking in design due
to the equipment abilities, compounding or
pressing the ingredients by force into a pellet
Today, this method is still used as there
are various values applied to the final product,
Economics apply even in aquaculture as
some species do not have the market value
for advanced feed production methods, or
simply they are not required for that species.
Extrusion does have advantages in formu-
lation abilities and in some cases the feeds
are actually less costly due to mainly the
reduced starch requirement in sinking feeds.
Less starch give more room for nutritional
building blocks allowing lower cost protein
uses in the feed.
As this industry in whole is advancing
technically other methods of feed production
emerged, mainly extrusion cooking. Why?
Initially, it was seen that the density of a
feed from an extrusion cooker was floating.
Researchers found they could monitor the fish
and feed consumption easily with the use of a
floating feed for many species in effect chang-
ing the feed pellet characteristics desired.
This effect was seen in the catfish indus-
try and others where additional advantages
including formulation cost reduction and feed
production methods allowed for feed cost
Thus, aquaculture became a business, a
big business, with entrepreneurs studying all
aspects of it.
Any advantage that could improve
the bottom line was of interest. Small
aquatic farmers with a few ponds turned
their operations into large 1000-hectare
farms, small feedmills turned into huge
bulk feed production plants, usually in
specially designed configurations.
The implication of change
Let’s review extrusion and the impli-
cations of changes effecting this indi-
vidual method of production.
A definition of extrusion cooking:
“Extrusion cooking is the process where
expandable biopolymers such as protein
and starch are plasticized in a tube by
a combination of heat, shear, and pres-
sure resulting in the denaturation of the
protein, the gelatinization of the starch,
and the exothermic expansion of the
Explained on the basis of aquatic feed
production expandable biopolymers,
starchy ingredients and functional pro-
by Joseph P. Kearns, Wenger Manufacturing, Inc, Sabetha, KS, USA
feeds by extrusion
Example of a
of Aquatic Feeds
34 | INTERNATIONAL AQUAFEED | March-April 2014
teins, are required to hold the pellets together
and to impart the needed ingredients to make
the feed float, sink slowly or sink rapidly.
Usually the starch requirement in extrusion
is in the 10 percent range for sinking and 20
percent range for floating.
Proteins are added for the nutritional
value with good quality functional proteins or
ones which have not been overheated before
extrusion also allow binding of the pellet.
Extrusion is usually a high temperature/short
time (HT/ST) process with extreme changes
occurring in the extruder barrel.
In about 30 seconds the powdery raw
material is melted into a plastic state by heat
via friction, shear by design of the barrel com-
ponents and pressure by forcing the material
through this device. T
he result is the final product. The question
is how to control all of these parameters and
make an individual feed or many different
styles of aquatic feeds with the same machine?
Historically, this process started out very
simply, that is what the industry had to offer,
simple but an advanced extruder which was
designed to expand products.
Honestly, these machines came from the
petfood industry and it just happened they
were the driver for extrusion in aquatic feed
applications. The industries mirrored each
other - believe it or not. At that time it was
typically eight to ten tons per hour
maximum capacity with restrictions.
Early on the restrictions were
how much fat or fresh meat can
be placed in the extruder as well
as capacity, smaller diameter feed
capacity, was greatly reduced when
compared to larger feed sizes. Pellet
of 15mm or larger were unheard of
and when someone asked for sinking
feeds, heads were scratched.
Over the years the petfood
industry asked for more fat in the
extruder, more fresh meat, density
control, control of the air cell sizes in
the pellets, more durable products to
mention a few.
Coincidentally, many of these top-
ics matched the questions from the
Let’s review these based on the flow
through an extruder.
Early on it was seen that the dry feed flow
rate to the extruder needed to be even. Same
for the liquids. If they varied the pressure in
the barrel changed and the expansion then
varied or yielded different diameter pellets.
Advancements of using loss-in-weight feed
systems advanced this area greatly, even
allowing for compensation while the bin emp-
ties at different fill levels. Dry ingredient flow
coupled with the liquid flows as a percentage
greatly increased the accuracy of complex
In other words as oils or fats, water, steam,
startup waste streams, ground meats and any
Large Capacity Single Screw Extruder for
Salmon and Floating Feed Applications, 17
tons per hour dry rate after extruder
Open Twin Screw Extruder Barrel. Discharge
on right where the plasticized mass is about
to exit the extruder. Shows the flow to
melted state phase changes
March-April 2014 | INTERNATIONAL AQUAFEED | 35
Turning ideas into opportunities.
PROGRESSIVE AQUAFEED PROCESSING
Imagine the possibilities
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Leave it to Wenger to redefine aquatic feed production
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barrel geometries that allow greater capacities than
any other extruder in its class.
The combined features allow increased production
capacity of up to 30 percent compared to previous
and competitive aquatic machines — totally
redefining cost/benefit. The TX-3000 can be equipped
with either the High Intensity Preconditioner (HIP) or
the High-Shear Conditioner (HSC) to match specific
process and capacity requirements, making it ideal
for processing a full range of aquatic feed products.
Contact us now. With new concepts and visionary
leadership, we’re ready to help you select
the right tools for your extrusion and
Our business in life is not to get ahead of others, but to get ahead of ourselves.
—Stewart B. Johnson, Dutch Artist
TX-3000 RAISES ThE BAR ON AQUATIC FEED PRODUCTION
Wenger14.TX3000.Ad.210x147.indd 1 4/9/14 7:34 AM
other solutions added could be done
very accurately. Tremendous improve-
ment as the mix became very exact
going into the extruder.
A major step forward in predict-
ability on the extrudate coming out
of the machine. All of this could be
done with flow meters and manual
operation. Computers are generally the
operations control method today for
advanced production and profitability.
Preconditioners, a standard device
on most extruders as well as pellet
mills, was the device that takes the
ingredients both dry and wet and
prepares them for the actual extruder
Many designs are available from
single cylinders, multiple cylinders and
dual shaft conditioners. All work as they
were designed for at the time.
Current technology would include
dual-shaft conditioners with each shaft
having speed and rotational control.
Residence time is considered one of
the main advancements between cyl-
Water and steam could always be
added, the question is how do you like
cleaning an extruder?
The older cylinder designs mixed
everything together but in some cases
the result was so sticky that flow from
the conditioner to the extruder barrel
stopped: The point downtime and
cleaning started. Newer designs over
the years, improved residence time,
eliminated this problem area as the
increased time allowed for absorption
of the liquids into the dry feed allowing
for a non-blocking, free-flowing powder
to easily flow into the extruder barrel.
The petfood industry pushed for
more meat addition which offered
advantages in the aquatic sector also.
The development of a High Intensity
Preconditioner, HIP, has allowed for
unsurpassed inclusion of protein sourc-
es such as terrestrial land
animal liquid streams or
ground up fish waste up
to 50 percent when mak-
ing a finished feed.
That is 50
percent meat and 50 percent cereal or
dry ingredients extruded into pellets.
Eighty-five percnet has been
achieved when extrusion of an ingredi-
ent is required. Combination of soy-
bean meal and fish waste dried to
be stored for future use, other dry
ingredients can be used also.
Extruder barrel advancements cent-
er on gaining control of the process as
well as increased capacities.
In the case where a single product
is made the extruder can be set up for
that application, such as a plant always
making salmon feed. Of course, there
can be differences within this sector
requiring modifications or various con-
trols to achieve the range of products
How about the aquatic feed manu-
facturer in an area where there are
numerous styles of feeds required? This
extruder application would require a
higher degree of flexibility to make all
the style feeds.
Tools to assist in
Buoyance of aquatic feeds still
receives attention and this is mainly
due to the fact that formulations are in
Price variations of ingredients and
the nutritional knowledge for the spe-
cies is most definitely moving aquatic
feeds to least cost formulations. As
more is known about the use of indig-
enous and wide varieties of ingredients
technology will assist the feed makers
in achieving the required feed densities.
Traditionally, the method for chang-
ing density is to modify the open area
of the extrusion die in relation to the
energy needed to cook and expand
the product. Low density requires less
open area and the opposite is true for
Imagine you make a feed and the
formulator modifies the formula slightly
for cost advantages and you have a
range of let’s say 50 formulas you
manufacture in various different diam-
eters. Different diameters have differ-
ent capacities and different rates of
expansion in each die design. Each is
Photo of small cell structure needed for vacuum
coated feeds for elevated oil content
0.5 mm Shrimp Feed, example of small diameter
Photo of a large diameter aquatic feed. Center
hole in pellet to aid in drying and digestion. Hole
can be left out for semi moist feed production for
large marine fish such as tuna
Sample off of a HIP Preconditioner, 50% fresh meat,
11.5% steam added, 3.4 minutes retention time and
a 35% moisture content. The perfect conditioned
free flowing powder ready for the extruder
Dual Drive, Speed and
36 | INTERNATIONAL AQUAFEED | March-April 2014
scheduled to be made depending on
the requirement by your clients. This is
almost an impossible situation to man-
Either you restrict the formulation
changes so as the extruder setup is well
defined for that product or you might
elect to use technical devices to assist
in the management of the required
equipment changes so the formulation
can move slightly due to market costs.
There are a number of devices
depending on your extruder supplier
that can assist in this area allowing
elevated flexibility while greatly reduc-
ing down time.
Flow restrictors in the extruder bar-
rel are designed to change the rate of
passage through the barrel.
Anytime you restrict the flow
you increase friction or energy input.
Increased energy input generally
increases expansion. Reduced energy
input or opening the barrel up for
easier flow makes the feed heavier or
less expanded. Where in the barrel to
place a device depends on the actual
The extruder barrel can be taken
apart and the screw configuration
changed to achieve flow restriction.
Devices have been developed to avoid
costly down time as much as possible
with the use of devices that can be
changed while running.
Typically they are used at the end
of the barrel or midway in the extruder
barrel thus Back Pressure Valves and Mid
Barrel Valves. Back Pressure Valves are
used at the end of the extruder and Mid
Barrel towards the center. Devices at the
end of the extruder usually assist in mak-
ing a difficult to float formula float easier.
Mid barrel valves are typically used
when making slow sinking or sinking
style feeds. Exceptions do exist as other
technology can be combined with the
above flow restricting devices.
In the case of requiring more open
area than traditional possible, design
changes with larger dies and cone head
designs has allowed for increased open
area greatly improving the capacity on
sinking feeds predominately the smaller
When controlling density the open
area is an important factor in the
floatability of the feed thus more open
area results in higher capacities on
sinking feeds. Larger extruders can also
do the job but if a smaller extruder
is used and achieve a higher rate the
investment cost just went down per
This photo shows a specialized C²TX, Conical
Twin Screw extruder for shrimp feed production,
notice the single shaft tapered conditioner, High
Shear Conditioner. Also show it the Oblique Tube
Die at the discharge with a Back Pressure Valve
Extruder Barrel with an Atmospheric Vent (shown
closed) and Manual hand crack operated Mid
Barrel Valve. Motorized version also available
March-April 2014 | INTERNATIONAL AQUAFEED | 37
Extruder OEE for the Production of Fish FeedExtruder OEE for the Production of Fish Feed
AMANDUS KAHL GmbH & Co. KG, Dieselstrasse 5-9, D-21465 Reinbek / Hamburg,
Phone: +49 40 727 71 0, Fax: +49 40 727 71 100, email@example.com www.akahl.de
The development of the Oblique Tube
Die has increased the open area by about
three times effectively allowing extruders
to achieve as an example four tons per
hour of sinking shrimp feeds of 1mm in
diameter. Technology is just starting that
can perhaps double this to the eight to
10 tons per hour on small diameter feeds
using traditional twin-screw extruders.
As mentioned above increased pressure in
the extruder barrel yields floating feeds. Thus
an early solution was to vent the barrel and
allow escape of pressure and some moisture
for sinking feeds. The result was an increase
Further developments showed that there
could be an advantage for pulling a vacuum
out of this vent to enhance the sinking effect.
This technology is used for aquatic feeds on
a limited basis when special combinations of
ingredients are passed through the extruder.
Typically this would be a mid-range fat level
Also discussed was the requirement of pet
food manufacturers to increase meat inclusion
levels. History has shown that cooking high
levels of fresh meat type products does not
work well in frictional designed extruders. The
challenge was met and the design of the ther-
mal twin-screw extrusion allowed 10 times
the steam inclusion moving the operational
conditions from frictional cook to thermal
cook allowing highly elevated meat
Feeds for farmed aquatic animals
will always need work to elevate
improvements and to handle the
new technology related to varie-
ties of ingredients so the industry
continues to move forward.
Recently, reviewing an article
by Mike Urch published in World
Fishing and Aquaculture (Jan. 13,
2014), he stated in the article on
cobia, “Cobia is a beautiful fish with
a firm, white flesh,”
Mr Myrseth says, “So we had
great hopes for it. But we did have
some production problems.
“It seemed to eat a lot, but at a
certain size it stopped growing or it
grew too slowly. So the feed factor
was very high and we had problems
making money on it.
“There seems to be a problem
with using dry feed for this fish.”
Right now work is progressing
on aquatic feeds with the Thermal
Twin-Screw design mentioned
Possible use for new technology
to change the way of making some
select marine fish feeding situations
viable. If you can take half the formula or so
and use ground waste aquatic material such
as head, frames etc and couple this with the
semi-moist concept of not drying the feeds,
then you can in effect make a soft feed that
has a texture that might be more conducive
to select species.
Tuna, cobia, grouper and other
marine fish might do well on different feed design
then what is traditionally available in dry form.
It must be better than feeding whole fish
which is considered not sustainable. It would
also allow for furthering the studies of what
they require nutritionally to allow reduced
feed cost and increase their acceptance as a
possibility for increased farming.
Terrestrial land animal waste products
should also be considered as protein sources
or as amino acid building blocks which in
some cases might partially replace the ever
decreasing availability of fish meal.
Salmon feed is a good example of improv-
ing feed techniques.
These feeds went from single digit oil levels
years ago to nearly 40 percent oil in the feeds
at this time. This caused a complete reversal
in equipment design. The industry went from
making sinking pellets off the extruder to
floating pellets which were then later infused
with oil via atmospheric coaters and later
with vacuum coaters for the extreme high oil
The oil added externally filled the air sacs
in the pellets eliminating the air resulting in
Communication between researchers and
equipment designers allowed for discussion
which resulted in the process we have today.
It was not that simple and one point that
stood out was keeping the oil in the pellets
after vacuum coating. Protein sponges need
to be made that did not release the oil in the
bag. Studies showed that energy input was the
key. Higher specific mechanical energy inputs
gave a smaller cell structure which hold the
Shrimp feeds is one that stands out as an
unusual feed. 100 percent sinking, good
water stability, small diameters and
Twin Screw Extruder complete with a Density
Management System, included vent and
vacuum pump system. For those mid-range fat
level sinking feeds, formula dependent
Thermal Twin Extruder making a high inclusion
level wet fish paste seen in tank to left pumped
into the HIP Conditioner at 50% of the capacity
38 | INTERNATIONAL AQUAFEED | March-April 2014
differences in formulations have shown that
special feed production equipment might be
the answer for this animal.
Single-screw extrusion has been used and is
still used in some areas. Everything needs to be
exact as any change in the formula can disrupt
the production. Twin-screw extrusion is more
forgiving in this case. Twin-screw extruders
are more positive pumping devices thus less
susceptible to screw wear changing the cook-
ing effect in the barrel. Not to mention the
need for pressure to shove feeds through die
holes which are sometimes in the 0.8mm and
above ranges. The above mentioned OTD was
designed for this sector specifically as well as
other micro feed diameters.
Traditional floating feeds is the most stable
of the aquatic sectors. Large capacities are
desired due to the low margin on catfish,
carp and tilapia feeds. In some cases these
feeds are easily formulated for the nutri-
tional aspects required however the struggle
is in filling the formula with inert or high fiber
lower cost ingredients. This is where devices
to impart more energy come into play as
discussed above. Also better grinding of the
fibrous ingredients do make extrusion easier.
Post extrusion processes
As one part of the process advances the
rest need to do the same to keep pace.
The two main areas here are drying and
coating. Dryers have advanced for better
and more even water removal, +/- 0.5 per-
cent moisture variance. Sanitary dryer designs
improve downtime for cleaning with easier
internal access. Floor space requirements are
reducing based on equipment designs.
Coating is another topic. High oil levels
use vacuum coating. Low oil levels use atmos-
Ever consider how to apply probiotic
or prebiotics as well as the other liquid
ingredients which are showing great interest?
At what percent are they applied? Real low
percentages? New atmospheric coaters with
control allow for low Coefficient of Variance
application down into the 0.5 percent applica-
Controls have had tremendous
Density check, moisture checks, NIR, photo
recognition, float or sinking rates and other
aspects can now be monitored on line and
computer control adjustment based on the
data for corrective action to move the process
back in the characteristic ranges needed.
In summary, the feed production support
industries for the aquaculture industry are in
the same exponential growth phase keeping
pace with the research and advancements in
this industry ensuring the needed improve-
ments for advancements.
Better cages, pond designs, water quality
systems, novel ingredients, the feeds them-
selves and the feed production equipment
are all moving forward as communication
between disciplines in this industry continue
to challenge each other to improve.
Atmospheric Coater for effective
external application of liquids from
0.5% to 8% to 10% range
Source Technologies Principal Device
to take samples in line while on
line for moisture, density and other
product attributes for advanced
equipment computer control
March-April 2014 | INTERNATIONAL AQUAFEED | 39
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Assessing the potential
of polychaete meal in
Prospects on dietary trace minerals
– aquafeeds & aquaculture
Volume 17 Issue 3 2014 - mAY | JuNe
FISH FARMING TECHNOLOGY
Use of a heat-stable
protease in salmonid feeds
– experiences from Canada and Chile
Fish Farming Technology supplement
Nets and cages
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